In the prior art, it is known to deposit a material onto a substrate via electron beam induced deposition (EBID) and ion beam induced deposition (IBID). According to the known method, a substrate is placed in the evacuable specimen chamber of a charged particle beam apparatus—typically either an electron beam (E-beam) system or a focused ion beam (FIB) system. The charged particle (or other) beam is applied to the substrate surface in the presence of a deposition gas, often referred to as a precursor gas. A layer of the precursor gas adsorbs to the surface of the work piece. The thickness of the layer is governed by the balance of adsorption and desorption of the gas molecules on the substrate surface, which in turn depends on, for example, the partial gas pressure (determining how many molecules are adsorbed per second), and the sticking coefficient (describing how long, on average, a molecule is adsorbed to the surface). The resultant layer is typically formed of one or several mono-atomic layers.
When the charged particle beam irradiates the substrate with the adsorbed layer of precursor gas, secondary electrons are emitted from the substrate. These secondary electrons as well as primary and backscattered electrons cause a dissociation of the adsorbed precursor gas molecules. Part of the dissociated precursor material forms a deposit on the substrate surface, while the rest of the precursor gas particle forms a volatile by-product and is pumped away by the vacuum system of the apparatus.
Beam induced deposition (BID) is used in a wide variety of applications for depositing a material onto a target surface of a substrate such as a semiconductor wafer or magnetic storage media. The materials are deposited for a variety of reasons such as to form thin-film surfaces, electrical connections, protective coatings for semiconductor feature characterization and analysis, or to “weld” small samples, such as TEM samples, to a manipulator or sample holder (as described in more detail below). Many combinations of gasses, substrates, and beam types can be used to achieve a variety of deposition schemes. The particular material to be deposited will usually depend on the application, underlying target surface, and how the material reacts with the beam or surface. Similarly, a variety of beam types can be used to generate secondary electrons, secondary ions, photons, phonons, plasmons, etc. These include ion, electron, and laser beams.
A disadvantage of known beam induced deposition methods is that while there are a wide variety of metals, semiconductors, and dielectrics that may be deposited using beam-induced techniques; the purity and material properties of BIDs are almost always much poorer than the bulk properties. This is widely documented in the prior art. One of the more common deposition material properties of concern is the metallic resistivity of deposits. Depending on the precursor and material deposited as well as the type of beam, resistivity values typically range from 10 to more than 1,000 times greater than the bulk metallic resistivity.
This increased resistivity of conductive materials deposited via BID is of special concern for circuit edit (CE) applications. Performing circuit edit using a FIB on an integrated circuit (IC) is essential for design debug and failure analysis. Today's high-frequency IC devices require very low interconnect resistivity for increased chip performance; resistivity on the order of 50 μΩ·cm is highly desirable to reduce any performance bottleneck resulting from on-chip interconnect delay. Application of the FIB circuit edits to validate performance of an IC device will be more effective if the resistivity of the edit closely approximates the values of the fabricated line. Using typical prior art methods, the lowest resistivity for a conductor deposited via IBID is tungsten having a resistivity value of ˜200 μΩ·cm, which is significantly greater than the desired 50 μΩ·cm resistivity for IC interconnects.
Accordingly, there is a need for an improved method of beam-induced deposition that provides for deposition of a conductor via BID having a lower resistivity—preferably a resistivity on the order of 50 μΩ·cm—than conductors deposited via prior art methods.